/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.http.converter.xml;

import java.io.IOException;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.Collection;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.SortedSet;
import java.util.TreeSet;

import javax.xml.bind.JAXBException;
import javax.xml.bind.UnmarshalException;
import javax.xml.bind.Unmarshaller;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlType;
import javax.xml.stream.XMLInputFactory;
import javax.xml.stream.XMLStreamException;
import javax.xml.stream.XMLStreamReader;
import javax.xml.transform.Result;
import javax.xml.transform.Source;

import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpInputMessage;
import org.springframework.http.HttpOutputMessage;
import org.springframework.http.MediaType;
import org.springframework.http.converter.GenericHttpMessageConverter;
import org.springframework.http.converter.HttpMessageConversionException;
import org.springframework.http.converter.HttpMessageNotReadableException;
import org.springframework.http.converter.HttpMessageNotWritableException;
import org.springframework.lang.Nullable;
import org.springframework.util.ReflectionUtils;
import org.springframework.util.xml.StaxUtils;

/**
 * An {@code HttpMessageConverter} that can read XML collections using JAXB2.
 *
 * <p>This converter can read {@linkplain Collection collections} that contain classes
 * annotated with {@link XmlRootElement} and {@link XmlType}. Note that this converter
 * does not support writing.
 *
 * @author Arjen Poutsma
 * @author Rossen Stoyanchev
 * @since 3.2
 */
@SuppressWarnings("rawtypes")
public class Jaxb2CollectionHttpMessageConverter<T extends Collection>
        extends AbstractJaxb2HttpMessageConverter<T> implements GenericHttpMessageConverter<T> {

    private final XMLInputFactory inputFactory = createXmlInputFactory();


    /**
     * Always returns {@code false} since Jaxb2CollectionHttpMessageConverter
     * required generic type information in order to read a Collection.
     */
    @Override
    public boolean canRead(Class<?> clazz, @Nullable MediaType mediaType) {
        return false;
    }

    /**
     * {@inheritDoc}
     * <p>Jaxb2CollectionHttpMessageConverter can read a generic
     * {@link Collection} where the generic type is a JAXB type annotated with
     * {@link XmlRootElement} or {@link XmlType}.
     */
    @Override
    public boolean canRead(Type type, @Nullable Class<?> contextClass, @Nullable MediaType mediaType) {
        if (!(type instanceof ParameterizedType)) {
            return false;
        }
        ParameterizedType parameterizedType = (ParameterizedType) type;
        if (!(parameterizedType.getRawType() instanceof Class)) {
            return false;
        }
        Class<?> rawType = (Class<?>) parameterizedType.getRawType();
        if (!(Collection.class.isAssignableFrom(rawType))) {
            return false;
        }
        if (parameterizedType.getActualTypeArguments().length != 1) {
            return false;
        }
        Type typeArgument = parameterizedType.getActualTypeArguments()[0];
        if (!(typeArgument instanceof Class)) {
            return false;
        }
        Class<?> typeArgumentClass = (Class<?>) typeArgument;
        return (typeArgumentClass.isAnnotationPresent(XmlRootElement.class) ||
                typeArgumentClass.isAnnotationPresent(XmlType.class)) && canRead(mediaType);
    }

    /**
     * Always returns {@code false} since Jaxb2CollectionHttpMessageConverter
     * does not convert collections to XML.
     */
    @Override
    public boolean canWrite(Class<?> clazz, @Nullable MediaType mediaType) {
        return false;
    }

    /**
     * Always returns {@code false} since Jaxb2CollectionHttpMessageConverter
     * does not convert collections to XML.
     */
    @Override
    public boolean canWrite(@Nullable Type type, @Nullable Class<?> clazz, @Nullable MediaType mediaType) {
        return false;
    }

    @Override
    protected boolean supports(Class<?> clazz) {
        // should not be called, since we override canRead/Write
        throw new UnsupportedOperationException();
    }

    @Override
    protected T readFromSource(Class<? extends T> clazz, HttpHeaders headers, Source source) throws IOException {
        // should not be called, since we return false for canRead(Class)
        throw new UnsupportedOperationException();
    }

    @Override
    @SuppressWarnings("unchecked")
    public T read(Type type, @Nullable Class<?> contextClass, HttpInputMessage inputMessage)
            throws IOException, HttpMessageNotReadableException {

        ParameterizedType parameterizedType = (ParameterizedType) type;
        T result = createCollection((Class<?>) parameterizedType.getRawType());
        Class<?> elementClass = (Class<?>) parameterizedType.getActualTypeArguments()[0];

        try {
            Unmarshaller unmarshaller = createUnmarshaller(elementClass);
            XMLStreamReader streamReader = this.inputFactory.createXMLStreamReader(inputMessage.getBody());
            int event = moveToFirstChildOfRootElement(streamReader);

            while (event != XMLStreamReader.END_DOCUMENT) {
                if (elementClass.isAnnotationPresent(XmlRootElement.class)) {
                    result.add(unmarshaller.unmarshal(streamReader));
                } else if (elementClass.isAnnotationPresent(XmlType.class)) {
                    result.add(unmarshaller.unmarshal(streamReader, elementClass).getValue());
                } else {
                    // should not happen, since we check in canRead(Type)
                    throw new HttpMessageConversionException("Could not unmarshal to [" + elementClass + "]");
                }
                event = moveToNextElement(streamReader);
            }
            return result;
        } catch (UnmarshalException ex) {
            throw new HttpMessageNotReadableException(
                    "Could not unmarshal to [" + elementClass + "]: " + ex.getMessage(), ex);
        } catch (JAXBException ex) {
            throw new HttpMessageConversionException("Could not instantiate JAXBContext: " + ex.getMessage(), ex);
        } catch (XMLStreamException ex) {
            throw new HttpMessageConversionException(ex.getMessage(), ex);
        }
    }

    /**
     * Create a Collection of the given type, with the given initial capacity
     * (if supported by the Collection type).
     *
     * @param collectionClass the type of Collection to instantiate
     * @return the created Collection instance
     */
    @SuppressWarnings("unchecked")
    protected T createCollection(Class<?> collectionClass) {
        if (!collectionClass.isInterface()) {
            try {
                return (T) ReflectionUtils.accessibleConstructor(collectionClass).newInstance();
            } catch (Throwable ex) {
                throw new IllegalArgumentException(
                        "Could not instantiate collection class: " + collectionClass.getName(), ex);
            }
        } else if (List.class == collectionClass) {
            return (T) new ArrayList();
        } else if (SortedSet.class == collectionClass) {
            return (T) new TreeSet();
        } else {
            return (T) new LinkedHashSet();
        }
    }

    private int moveToFirstChildOfRootElement(XMLStreamReader streamReader) throws XMLStreamException {
        // root
        int event = streamReader.next();
        while (event != XMLStreamReader.START_ELEMENT) {
            event = streamReader.next();
        }

        // first child
        event = streamReader.next();
        while ((event != XMLStreamReader.START_ELEMENT) && (event != XMLStreamReader.END_DOCUMENT)) {
            event = streamReader.next();
        }
        return event;
    }

    private int moveToNextElement(XMLStreamReader streamReader) throws XMLStreamException {
        int event = streamReader.getEventType();
        while (event != XMLStreamReader.START_ELEMENT && event != XMLStreamReader.END_DOCUMENT) {
            event = streamReader.next();
        }
        return event;
    }

    @Override
    public void write(T t, @Nullable Type type, @Nullable MediaType contentType, HttpOutputMessage outputMessage)
            throws IOException, HttpMessageNotWritableException {

        throw new UnsupportedOperationException();
    }

    @Override
    protected void writeToResult(T t, HttpHeaders headers, Result result) throws IOException {
        throw new UnsupportedOperationException();
    }

    /**
     * Create an {@code XMLInputFactory} that this converter will use to create
     * {@link javax.xml.stream.XMLStreamReader} and {@link javax.xml.stream.XMLEventReader}
     * objects.
     * <p>Can be overridden in subclasses, adding further initialization of the factory.
     * The resulting factory is cached, so this method will only be called once.
     *
     * @see StaxUtils#createDefensiveInputFactory()
     */
    protected XMLInputFactory createXmlInputFactory() {
        return StaxUtils.createDefensiveInputFactory();
    }

}
